Accuracy of virtual non-contrast images from dual-energy integrating detector CT and photon-counting detector CT at high iodine concentrations

ObjectivesTo evaluate virtual non-contrast (VNC) accuracy at multiple radiation doses and iodine concentrations in a head CT phantom using dual-energy integrating-detector CT (EID-CT; TwinSpiral DECT) and photon-counting detector CT (PCD-CT).Materials and MethodsA cylindrical head-sized acrylic CT phantom with brain tissue inserts and iodine (0, 43.75, 175, and 350 mg/mL; 87.5 mg/mL was excluded due to beam-hardening artifacts) was scanned three times on each system at 100%, 80%, 75%, 65%, 50%, and 25% of the standard radiation dose to generate mixed and VNC images. Attenuations (HU) were measured in standard and corresponding VNC images; signed and absolute VNC errors were analyzed with two-way ANOVA (dose, iodine) with Tukey post hoc tests (<i>p</i> < .05), using nonparametric alternatives when assumptions were violated. Phantom HU for fat, bone, and white matter at 100% dose on EID-CT were compared with 16 patient scans to confirm realism.ResultsRadiation dose significantly affected VNC errors in both scanners, but only 25% versus 100% dose in PCD-CT was significant after Tukey (<i>p</i> = .0383); no pairwise dose differences were significant in EID-CT (<i>p</i> ≥ .07). Iodine concentration had a stronger effect. In EID-CT, 350 mg/mL differed from 0, 43.75, and 175 mg/mL (<i>p</i> < .001), with errors up to +13.7 ± 1.1 HU. In PCD-CT, 175 and 350 mg/mL differed from 0 mg/mL (<i>p</i> < .05) and from 43.75 mg/mL (<i>p</i> < .001), with a negative bias up to -10.6 ± 1.5 HU.ConclusionsDose reduction had limited impact on VNC accuracy, whereas high iodine (175-350 mg/mL) caused significant errors with opposite signed biases (EID-CT overestimation, PCD-CT underestimation). Both scanners still achieved substantial visual contrast removal.